According to Stoke’s Law for settling velocity of small particles and viscous flow.

1. \({v_s} = \frac{g}{{18}}.\left( {G - 1} \right).\frac{d}{v}\)

2. \({v_s} = \frac{g}{{18}}.\left( {G - 1} \right).\frac{{{d^2}}}{v}\)

3. \({v_s} = \frac{{18}}{g}.\left( {G - 1} \right).\frac{{{d^2}}}{v}\)

4. \({v_s} = \frac{g}{{18}}.\left( {G + 1} \right).\frac{{{d^2}}}{v}\)